It seems to me that there simply has to be a better way of doing this, but i still haven't found one. And i'm sure i'm not the only one who could use a way to do this: Run an SQL query that only produces one field in one row, then assign that field to a scalar. (In my case, if the query results in more than one field/row, then i have bigger things to worry about than the script breaking).
For example, to get the timestamp from the SQL server, one could use:
my $timestamp;
my $cmd = $dbh->prepare('SELECT cast(now() AS timestamp);') or die $!;
$cmd->execute();
while (my #asd = $cmd->fetchrow_array) { $timestamp = $asd[0] }
Dirty, but it works. But using 4 lines seem a bit much for a simple assignment, especially considering how well perl and postgresql can communicate with eachother via DBI. Sure, i could write a subroutine for it, but isn't there something native that allows me to fetch data as easily as i submit data with $dbh->do() ?
And yes, i did try google.
Usually I write:
$value = $dbh->selectall_arrayref($sql)->[0]->[0];
There's always selectrow_array:
selectrow_array
#row_ary = $dbh->selectrow_array($statement);
#row_ary = $dbh->selectrow_array($statement, \%attr);
#row_ary = $dbh->selectrow_array($statement, \%attr, #bind_values);
This utility method combines prepare, execute and fetchrow_array into a single call.
So something like this:
my $timestamp = $dbh->selectrow_array('select cast(now() as timestamp)');
There's also selectrow_arrayref and selectrow_hashref for similar situations.
From perldoc DBI:
"selectrow_arrayref"
$ary_ref = $dbh->selectrow_arrayref($statement);
$ary_ref = $dbh->selectrow_arrayref($statement, \%attr);
$ary_ref = $dbh->selectrow_arrayref($statement, \%attr, #bind_values);
This utility method combines "prepare", "execute" and
"fetchrow_arrayref" into a single call. It returns the first row of
data from the statement. The $statement parameter can be a previously
prepared statement handle, in which case the "prepare" is skipped.
If any method fails, and "RaiseError" is not set, "selectrow_array"
will return undef.
That will get you most of the way. You still need to do some error checking, but you would be doing that anyway.
Wouldn't fetchrow_array actually only return a scalar as you're only asking for one column?
Related
I have been trying to get perl subroutine value and substitution to get the required part of string from randomips subroutine in exim.conf. However when i use string substitution i get error as follow:
Here is what I am trying to achieve
I am trying to split string by colon and get first occurrence as "interface". I'll be using second occurrence as the "helo_data.
exim.pl
sub randomhosts {
#inet = ("x.x.x.1:hostname1.domain.com","x.x.x.2:hostname2.domain.com","x.x.x.3:hostname3.domain.com"
);
return $inet[int rand($#inet+1)];
}
exim.conf
dkim_remote_smtp:
driver = smtp
interface = "${perl{randomhosts}%:*}"
helo_data = "${sender_address_domain}"
Error I get is as follow:
"failed to expand "interface" option for dkim_remote_smtp transport: missing '}' after 'perl'".
Probably the syntax.
Any help?
The code that you are trying to copy was written by someone who doesn't know much about Perl. It includes this line:
return $inet[int rand($#inet+1)];
A Perl programmer would write this as
return $inet[rand #inet];
I think there are a couple of issues here - one with your Exim syntax and one with your Perl syntax.
Exim is giving you this error:
failed to expand "interface" option for dkim_remote_smtp transport: missing '}' after 'perl'
I don't know anything about calling Perl from Exim, but this page mentions a syntax like ${perl{foo}} (which is similar to the one used in the page you are copying from) and one like ${perl{foo}{argument}} for calling a subroutine and passing it an argument. Nowhere does it mention syntax like yours:
${perl{randomhosts}%:*}
I'm not sure where you have got that syntax from, but it seems likely that this is what is causing your first error.
In a comment, you say
I am stying to get first part of string before colon for each random array value for "interface" and part after colon for "helo_data"
It seems to me that Exim doesn't support this requirement. You would need to call the function twice to get the two pieces of information that you require. You might be able to do this in the Perl using something like state variables - but it would be far more complex than the code you currently have there.
Secondly, your Perl code has a syntax error, so even if Exim was able to call your code, it wouldn't work.
The code you're copying sets up #inet like this:
#inet = ("x.x.x.1", "x.x.x.2", "x.x.x.3", "x.x.x.4");
Your equivalent code is this:
#inet = (
"x.x.x.1:hostname1.domain.com",
"x.x.x.2:hostname2.domain.com,
x.x.x.3:hostname3.domain.com
);
I've reformatted it, to make the problems more obvious. You are missing a number of quote marks around the elements of the array. (Note: I see that while I have been writing this answer, you have fixed that.)
Update: Ok, here is some code to put into exim.pl that does what you want.
use feature qw[state];
sub randomhosts {
state $current;
my #inet = (
"x.x.x.1:hostname1.domain.com",
"x.x.x.2:hostname2.domain.com",
"x.x.x.3:hostname3.domain.com"
);
if ($_[0] eq 'generate') {
shift;
#{$current}{qw[ip host]} = split /:/, $inet[rand #inet];
}
return $current->{$_[0]};
}
It generates a new ip/host pair if its first argument is 'generate'. It will then return either the hostname or the ip address from the generated pair. I think you can probably call it from your Exim config file like this:
dkim_remote_smtp:
driver = smtp
interface = "${perl{randomhosts}{generate}{ip}}"
helo_data = "${perl{randomhosts}{host}}"
But I'm no expert in Exim, so that syntax might need tweaking.
First I would like to note I have not worked with exim so I cannot say what exactly you are trying to do and why you have done things exactly so.
In the link you posted, a method called 'randinet' is added to exim.pl and the interface line in exim.conf is replaced by
interface = "${perl{randinet}}"
You have implemented a 'randomhosts' method and replaced the interface line with
interface = "${perl{randomhosts}%:*}"
Now the parser complains about not finding the closing bracket. That is likely due to the symbols you felt free to add but the parser does not have the freedom to ignore.
I suggest you try
interface = "${perl{randomhosts}}"
I wrote a procedure which imports data from an xml-file into a MariaDB using library DBI. The procedure works but I don't understand why the following code gives me the message:
use of uninitialized value $DBI::err in concatenation (.) or string at ...
Here the code (abbreviated):
my $insert_art = $dbh->prepare(
"INSERT INTO odbb_articles (creation_dt,ref_data,comp_no)".
"VALUES (?,?,?)"
);
....
my $comp_no = $xpc->findvalue('./sr:ARTCOMP/sr:COMPNO',$node1);
....
$insert_art->execute($creation_dt,$ref_data,$comp_no)
or die "Fehler bei der Ausfuehrung: ".
"$DBI::err -> $DBI::errstr (odbb_articles $DBI::state)\n";
If I insert the code
if ($comp_no eq "") { $comp_no = undef; }
just before $insert_art->execute the procedure works. This error happens when there is no entry in the xml-file for element COMPNO. I can avoid it if I define it as undef. I just wonder
why $comp_no cause this problem and
is there another solution than to control if $comp_no is "" and define it as undef?
The reason for the second question is to avoid the if statement if there are a lot of variables/columns which may have empty entries.
Thanks for help.
use of uninitialized value $DBI::err in concatenation (.) or string at ...
The error message you are seeing is Perl telling you that $DBI::err is undef. That is not because of the value of your $comp_no. It's just a result of what your program is doing.
So when you pass an empty string to the comp_no column, the database doesn't like that. It throws an error. DBI catches that error and passes it on. The $insert_art->execute returns a false value and the right-hand-side of the or gets called. That's your die.
Now in the string that you pass to die you put three variables:
$DBI::err
$DBI::errstr
$DBI::state
According to the DBI documentation, those are equivalent to the functions $h->err, $h->errstr and $h->state with $h being the last handle used. Let's look at the docs for those.
$h->err
Returns the native database engine error code from the last driver method called. The code is typically an integer but you should not assume that.
The DBI resets $h->err to undef before almost all DBI method calls, so the value only has a short lifespan. Also, for most drivers, the statement handles share the same error variable as the parent database handle, so calling a method on one handle may reset the error on the related handles. [...]
This does not explain when it can be undef.
$h->errstr
Returns the native database engine error message from the last DBI method called. This has the same lifespan issues as the "err" method described above.
The returned string may contain multiple messages separated by newline characters.
The errstr() method should not be used to test for errors, use err() for that, because drivers may return 'success with information' or warning messages via errstr() for methods that have not 'failed'.
Ok, so this is text. Don't use it to test for specific errors. You're not doing that. You just want to give debug output when the program fails.
$h->state
Returns a state code in the standard SQLSTATE five character format. Note that the specific success code 00000 is translated to any empty string (false). If the driver does not support SQLSTATE (and most don't), then state() will return S1000 (General Error) for all errors.
The driver is free to return any value via state, e.g., warning codes, even if it has not declared an error by returning a true value via the "err" method described above.
The state() method should not be used to test for errors, use err() for that, because drivers may return a 'success with information' or warning state code via state() for methods that have not 'failed'.
Again, this is not very clear about how useful it is.
My advice is to get rid of $DBI::err and $DBI::state. You don't need those to figure out what the problem is. Just output $DBI::errstr.
$insert_art->execute($creation_dt,$ref_data,$comp_no)
or die "Fehler bei der Ausfuehrung: " . $dbh->errstr;
Now your program will still fail, but at least you will have a meaningful error message that will explain what your database didn't like about the statement. That's better than being told how there is a bug in your error handling code.
Afterwards, the other answers will probably apply to fix the reason this is happening in the first case.
On another note, a word on die: If you provide a \n at the end of your arguments, it will not print your current script, line number and input handle line number. But those might be useful in your case. You can include them.
In a SQL database an empty string is very different to null.
If comp_no has a foreign key pointing to a record in another table, then the value "" is an accettable one only if there is a record with "" as primary key, very improbable.
Yu can fix this converting empty values to undef:
for ($creation_dt,$ref_data,$comp_no ){
defined $_ and $_ eq '' and $_ = undef;
}
$insert_art->execute($creation_dt,$ref_data,$comp_no);
or also
$insert_art->execute(map {defined($_) && length($_) ? $_ : undef} ($creation_dt,$ref_data,$comp_no));
This is a possible shortcut:
$comp_no ||= undef;
With the caveat that this will work in any case where $comp_no evaluates as false, meaning a value of 0 will actually cause the result to go undef also, which may or may not matter to you. If your field is numeric, I'd say it matters a lot.
When I use the same request in mySQL Workbench, the count of results is 41100.
In my script, the count is 1015. I have no error in my code (I use die for see it).
What is the cause of this difference?
# Create the statement
# select all id in table contacts
$statement = "select distinct contacts.id from $database.contacts";
# Prepare and execute the SQL query
$sqlQuery = $connectGrc->prepare($statement)
# Execute the statement
$sqlQuery->execute()
# Make id in array
while($oneId = $sqlQuery->fetchrow_array())
{
push(#ArrayId,$oneId);
}
There's nothing obviously wrong (except for the lack of error checking and that your comments are not program comments). Try connecting with RaiseError on, 'use strict;', and see if there are problems which you otherwise might not see. Also, if all you want is a one-column array of results, and can settle for an array reference, consider selectcol_arrayref() for convenience.
I searched SO before asking this question, I am completely new to this and have no idea how to handle these errors. By this I mean Perl language.
When I put this
%name->{#id[$#id]} = $temp;
I get the error Using a hash as a reference is deprecated
I tried
$name{#id[$#id]} = $temp
but couldn't get any results back.
Any suggestions?
The correct way to access an element of hash %name is $name{'key'}. The syntax %name->{'key'} was valid in Perl v5.6 but has since been deprecated.
Similarly, to access the last element of array #id you should write $id[$#id] or, more simply, $id[-1].
Your second variation should work fine, and your inability to retrieve the value has an unrelated reason.
Write
$name{$id[-1]} = 'test';
and
print $name{$id[-1]};
will display test correctly
%name->{...}
has always been buggy. It doesn't do what it should do. As such, it now warns when you try to use it. The proper way to index a hash is
$name{...}
as you already believe.
Now, you say
$name{#id[$#id]}
doesn't work, but if so, it's because of an error somewhere else in the code. That code most definitely works
>perl -wE"#id = qw( a b c ); %name = ( a=>3, b=>4, c=>5 ); say $name{#id[$#id]};"
Scalar value #id[$#id] better written as $id[$#id] at -e line 1.
5
As the warning says, though, the proper way to index an array isn't
#id[...]
It's actually
$id[...]
Finally, the easiest way to get the last element of an array is to use index -1. The means your code should be
$name{ $id[-1] }
The popular answer is to just not dereference, but that's not correct. In other words %$hash_ref->{$key} and %$hash_ref{$key} are not interchangeable. The former is required to access a hash reference nested as an element in another hash reference.
For many moons it has been common place to nest hash references. In fact there are several modules that parse data and store it in this kind of data structure. Instantly depreciating the behavior without module updates was not a good thing. At times my data is trapped in a nested hash and the only way to get it is to do something like.
$new_hash_ref = $target_hash_ref->{$key1}
$new_hash_ref2 = $target_hash_ref->{$key2}
$new_hash_ref3 = $target_hash_ref->{$key3}
because I can't
foreach my $i(keys(%$target_hash_ref)) {
foreach(%$target_hash_ref->{$i} {
#do stuff with $_
}
}
anymore.
Yes the above is a little strange, but creating new variables just to avoid accessing a data structure in a certain way is worse. Am I missing something?
If you want one item from an array or hash use $. For a list of items use # and % respectively. Your use of # as a reference returned a list instead of an item which perl may have interpreted as a hash.
This code demonstrates your reference of a hash of arrays.
#!/usr/bin perl -w
my %these = ( 'first'=>101,
'second'=>102,
);
my #those = qw( first second );
print $these{$those[$#those]};
prints '102'
I'm working with perl, and using DBI. Up to now, I've been using ->fetchall_arrayref to get the results of a database query, and just accessing the array by numeric keys. However, I much prefer to be able to access records by the field names (associative fetch) than numeric.
How do I do this, and what is the correct syntax for accessing the keys?
I would prefer something like:
$data[0]['name']
Instead of:
$data[0][1]
Working Solution
my %data;
#{$data{$id}}{('name')} = 'something';
Read the DBI docs. Particularly, fetchall_hashref.
And you should also learn Perl syntax, as it's not the same as PHP.
You can use selectall_arrayref for this. Here's example from the DBI manpage:
You may often want to fetch an array of rows where each row is stored as a hash.
That can be done simple using:
my $emps = $dbh->selectall_arrayref(
"SELECT ename FROM emp ORDER BY ename",
{ Slice => {} }
);
foreach my $emp ( #$emps ) {
print "Employee: $emp->{ename}\n";
}
If you do fetchall_hashref() then you get the hash you are looking for. The keys will be the field names from the database. I am a little late, and Joe got it, but it will be.
$data->{0}->{'field'};